This application relies for priority upon Korean Patent Application No. 2000-69983, filed on Nov. 23, 2000 and Korean Patent Application No. 2001-11055, filed on Mar. 3, 2001, the contents of which are herein incorporated by reference in their entirety.
The present invention relates to an apparatus for manufacturing a semiconductor wafer and method therefor, and more particularly to an apparatus for polishing a semiconductor wafer and method therefor.
As the elements incorporated into a semiconductor device are increasingly integrated, the structure of device wires such as gate lines and bit lines continues to become multiple-layered. For this reason, step coverage between unit cells on a semiconductor substrate is increased. To reduce the step coverage between the unit cells, various methods of polishing a wafer have been developed. Among these methods, a chemical-mechanical polishing (CMP) method which planarizes the surface of the wafer in the fabrication is widely used.
In a general CMP process, a polishing head of a CMP apparatus secures a wafer using a vacuum or surface tension and loads the wafer on an abrasive pad of a turntable. The polishing head imposes a controllable load on the wafer to hold it in tight contact with the abrasive pad. Thereafter, the polishing head is rotated to rotate the wafer with respect to the abrasive pad of the turntable.
In order to increase the efficiency of the CMP process, the wafer should be polished at a high speed while maintaining uniform flatness. However, characteristics such as uniformity, flatness and polishing speed of the wafer are highly dependent on relative speed between the wafer and the abrasive pad, as well as the force or load of the polishing head urging the wafer against the abrasive pad. Particularly, the larger the force imposed on the wafer by the polishing head against the abrasive pad, the faster the polishing speed. Accordingly, in the case where an uneven load is imposed on the wafer by means of the polishing head, a portion of the wafer on which relatively large force is imposed will be polished at a faster rate than other portions of the wafer on which relatively small force is imposed.
Generally, the polishing head includes a flexible membrane which is adapted to pick up and release the by vacuum. However, the vacuum between the membrane and the wafer is often leaked, such that during transfer, the wafer may be dropped or otherwise harmed.
To address these limitations, a polishing head with a modified structure has been proposed, which chucks/releases a wafer via vacuum holes formed at bosses that protrude from a chucking supporter of the head. However, such a polishing head introduces limitations that are shown in FIG. 1, which is a graph illustrating the resulting uneven surface of a wafer. In FIG. 1, reference character A indicates a wafer portion corresponding to the protruded bosses and reference character B indicates a wafer corresponding to a step projected from an edge of the supporter. Portions A and B are relatively over-polished as compared to other portion of the wafer, thereby compromising the uniformity of polishing surface of the wafer.
It is an object of the present invention to provide an improved apparatus for polishing a semiconductor wafer and method therefor which can provide high polishing uniformity.
It is another object of the present invention to provide an improved apparatus for polishing a semiconductor wafer and method therefor which can individually control pressure to be imposed on each of certain areas of the wafer in a polishing process.
It is other object of the present invention to provide an improved apparatus for polishing a semiconductor wafer and method therefor which can individually control polishing speed of each of certain areas of the wafer in a polishing process.
It is further object of the present invention to provide an improved apparatus for polishing a semiconductor wafer and method therefor, having a polishing head which can stably pick up the wafer.
It is still other object of the present invention to provide an improved apparatus for polishing a semiconductor wafer and method therefor, which can prevent scratches from being generated by the polishing head due to cleansing slurry particles flowing between membranes and supporters during the polishing process.
These and other objects are provided, according to the present invention, by an apparatus for polishing a semiconductor wafer comprising a supporting portion having an abrasive pad disposed thereon, and a polishing head disposed over the abrasive pad. The polishing head comprises a dish shaped carrier, a retainer ring disposed on a lower edge of the carrier, a supporter disposed in the carrier to provide first and second chambers separated from each other, and a membrane enclosing a surface portion of the supporter to be able to be expanded and spaced apart from the surface portion.
In a preferred embodiment, the surface portion of the supporter has a flat surface and a plurality of first and second holes formed therein to communicate with the first and second chambers. The membrane has a plurality of third holes corresponding to the first holes.
Films are adhered on the flat surface around the first holes. Each of the films is sized so as to be inserted into the corresponding third hole and thickness less than, or equal to, that of the membrane. Also, an edge of the surface portion of the supporter can be chamfered or rounded.
In the embodiment, one of the second holes is formed in a center portion of said supporter, and there is no hole formed in a portion of the membrane corresponding to the one second hole. According to another aspect of the present invention, there is provided an apparatus for polishing a wafer including a polishing head comprising: a carrier, a retainer ring disposed on a lower edge of the carrier, a supporter disposed in the carrier to provide a first chamber, a membrane enclosing a surface portion of the supporter to be able to be expanded and spaced apart from the surface portion, and a chucking ring for taking the wafer up by vacuum disposed on a lower portion the carrier to provide a second chamber.
In a preferred embodiment, the supporter has a plurality of first holes formed in a surface portion thereof to communicate with the first chamber, and the chucking ring has a plurality of second holes formed therein to communicate with the second chamber. Films are adhered on the chucking ring around the second holes to act as a medium in taking up or taking up and releasing of the wafer. The first and second chambers can have first and second fluid passages communicating external to the polishing head.
In the embodiment, the polishing head further includes a manifold for supplying air or fluid, or vacuum, from the outside of the polishing head to the first and second fluid passages, and a first elastic member for moving elastically the carrier up and down by means of air or vacuum supplied from the manifold, disposed between the manifold and the carrier.
According to other aspect of the present invention, there is provided an apparatus for polishing a semiconductor wafer including a polishing head comprising: a dish shaped carrier, a retainer ring disposed on an lower edge of the polishing head, having a space for receiving the wafer, a center supporter disposed in the carrier to provide a first chamber, a middle supporter disposed in the carrier on the same plane as the center supporter is disposed, to provide a second chamber, first and second membranes enclosing the center and middle supporters to be able to be separated from surface portions of the supporters, and a chucking ring disposed in the carrier to provide a third chamber.
In a preferred embodiment, a plurality of first holes are formed in the surface portion of the center supporter to communicate with the first chamber, a plurality of second holes are formed in the surface portion of the middle supporter to communicate with the second chamber, and a plurality of third holes are formed in the chucking ring to communicate with the third chamber.
In the embodiment, the chucking ring can be disposed between the center supporter and the middle supporter. Alternatively, the chucking ring can be disposed between the middle supporter and an inner surface of the carrier. The first, second and third chambers can have first, second and third fluid passages communicating external to the polishing head, respectively. Also, the middle supporter and the second membrane can be composed of ring shapes.
According to further aspect of the present invention, there is provided a method for polishing a wafer for use in an apparatus comprising a supporting portion having an abrasive pad disposed thereon; a polishing head disposed over the abrasive pad; and the polishing head comprising a carrier, a supporter disposed in the carrier to provide first and second chambers separated from each other, including a surface portion having a flat surface and a plurality of first and second holes formed therein to communicate with the first and second chambers, and a membrane enclosing a surface portion of the supporter to be able to be expanded and spaced apart from the surface portion, having a plurality of third holes corresponding to the first holes, comprising the step of positioning the membrane on a first surface of the wafer, taking the wafer up by making the first and second chambers communicating with the first and second holes vacuous or respectively vacuous and at atmospheric pressure to absorb and hold the wafer through the third holes, positioning the wafer on the abrasive pad to allow a second surface of the wafer to be in contact with the abrasive pad, expanding the membrane to impose load on the wafer by inputting air into the membrane through the first and second holes into the membrane, and polishing the second surface of the wafer by rotating the polishing head.
The method further includes the steps drawing the wafer upwardly by making the first and second chambers communicating with the first and second holes vacuous, or respectively vacuous and at atmospheric pressure, to absorb and hold the wafer through the third holes after the polishing step, and unloading the wafer from the polishing pad.
According to still other aspect of the present invention, there is provided a method for polishing a wafer for use in an apparatus comprising a dish shaped carrier, a retainer ring disposed on an lower edge of the polishing head, having a space for receiving the wafer, a center supporter disposed in the carrier to provide a first chamber communicating with a plurality of first holes, a middle supporter disposed in the carrier on the same plane as the center supporter is disposed, to provide a second chamber communicating with a plurality of second holes, first and second membranes enclosing the center and middle supporters to be able to be separated from surface portions of the supporters, and a chucking ring disposed in the carrier to provide a third chamber communicating with a plurality of third holes, comprising the step of positioning the chucking ring on a first surface of the wafer, drawing the wafer upwardly by making the first and second chambers communicating with the first and second holes vacuous or at atmospheric pressure, and the third chamber communicating with the third holes vacuous to absorb and hold the wafer through the third holes, positioning the wafer on the abrasive pad to allow a second surface of the wafer to be in contact with the abrasive pad, expanding the first and second membranes to impose load on the wafer by inputting air into the first and second membranes through the first and second holes, inputting air through the third holes to impose pressure on the first surface of the wafer, and polishing the second surface of the wafer by rotating the polishing head.
The method further includes the steps of taking the wafer up by making the first and second chambers communicating with the first and second holes vacuous or at atmospheric pressure, and the third chamber communicating with the third holes vacuous to absorb and hold the wafer through the third holes after the polishing step, and unloading the wafer from the polishing pad.